title: Divalent cations can induce the exposure of GroEL hydrophobic surfaces and strengthen GroEL hydrophobic binding interactions. Novel effects of Zn2+ GroEL interactions.
abstract: Fluorescent and non-fluorescent probes have been used to show that divalent cations (Ca2+, Mg2+, Mn2+, and Zn2+) significantly increase hydrophobic exposure on GroEL, whereas monovalent cations (K+ and Na+) have little effect. Zn2+ always induced the largest amount of hydrophobic exposure on GroEL. By using a new method based on interactions of GroEL with octyl-Sepharose, it was demonstrated that Zn2+ binding strengthens GroEL hydrophobic binding interactions and increases the efficiency of substrate release upon the addition of MgATP and GroES. The binding of 4, 4'-bis(1-anilino-8-naphthalenesulfonic acid) to GroEL in the presence of Zn2+ has a Kd congruent with 1 microM, which is similar to that observed previously for the GroEL 4, 4'-bis(1-anilino-8-naphthalenesulfonic acid) complex. Urea denaturation, sedimentation velocity ultracentrifugation, and electron microscopy revealed that the quaternary structure of GroEL in the presence of Zn2+ had a stability and morphology equivalent to unliganded GroEL. In contrast, circular dichroism suggested some loss in both alpha-helical and beta-sheet secondary structure in the presence of Zn2+. These data suggest that divalent cations can modulate the amount of hydrophobic surface presented by GroEL. Furthermore, the influence of Zn2+ on GroEL hydrophobic surface exposure as well as substrate binding and release appears to be distinct from the stabilizing effects of Mg2+ on GroEL quaternary structure.
authors.affiliation: Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78284-7760, USA.
authors.forename: B T
authors.initials: BT
authors.lastname: Brazil
authors.forename: J
authors.initials: J
authors.lastname: Ybarra
authors.forename: P M
authors.initials: PM
authors.lastname: Horowitz
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002413:Cations, Divalent; D018835:Chaperonin 10 / Q000378:metabolism; D018834:Chaperonin 60 / Q000737:chemistry / Q000378:metabolism*; D002942:Circular Dichroism; D008274:Magnesium / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013499:Surface Properties; D015032:Zinc / Q000378:metabolism*
chemical_list: D002413:Cations, Divalent; D018835:Chaperonin 10; D018834:Chaperonin 60; D008345:Manganese; D000255:Adenosine Triphosphate; D008274:Magnesium; D015032:Zinc; D002118:Calcium